EGR Vacuum Modulator Meltdown following EGT Delete (1 Viewer)

[sjpitts]

93 FJZ80--LandCruiser-- Federal Spec

So a couple of months ago I noticed that some vacuum hoses on my engine were cracked and coming apart. Who knows how long they had been that way. After researching I discovered that these were EGR vacuum hoses-- hoses that go between the EGR vacuum modulator and the intake. At first I was just going to replace the hoses, but after reading a bunch of threads on the damage that the EGR pipe can do the electrical wiring I decided to just "turn off" the EGR by rerouting the hoses.

Basically, I followed this thread:
'94 Code 71, EGR Bypass and redneck technique..

That thread shows how you can "delete" the EGR by just looping one hose back to the EGR vacuum modulator and looping the other hose back to to the intake.

These are pictures from that thread:

Note that I didn't do anything electrical, because my understanding is that on a 93 the EGR system can be deleted without throwing a code.

Well I opened the hood today and noticed that my EGR vacuum modulator had "exploaded" for lack of a better word. The hoses I had looped were blown off, and the hose underneath that goes to the EGR valve was just gone.

The check engine light is not on. I had noticed a smell at one time, but I thought that was just my leaking valve cover gasket dripping on something. I had noticed a lack of power the last time I was pulling a trailer, but I don't know if that was related.

So what happened here? Did my EGR delete cause this? I did see a thread that said this could be caused by bad cats, so maybe this is just a coincidence.

So what should I do here? I really would prefer to keep that EGR system off if I can. But I need it pass the visual inspection when the time comes.

Thanks

Jared

 

[Pin_Head]

Melted and burned out modulators are due to increased exhaust gas pressure and flow. This is often due to a clogged exhaust system, such as a clogged catalyst.

 

[sjpitts]

Melted and burned out modulators are due to increased exhaust gas pressure and flow. This is often due to a clogged exhaust system, such as a clogged catalyst.

So the theory is that clogged cats lead to increase backpressure-- and that increased backpressure is pushed out the EGR pipe, where it blows out through the EGR valve and into the EGR vacuum modulator, and that make the EGR valve melt.

And all this can happen whether or not I have "deleted" or turned off the EGR by looping the vacuum the hoses?

That does make sense to me.

Is there a way to test the cats? Does that mean that the EGR valve is probably leaking hot gases into the engine bay and needs to be replaced, even if I plan to keep the EGR system turned off?

Jared

 

[Tools R Us]

It could be from excessive exhaust back pressure. But, the melted ones we have seen were from the diaphragm in the modulator failing/leaking, allowing hot exhaust into the upper chamber, melting it. In your case, try plugging off the lower, exhaust line, may solve the problem. If the plug keeps blowing off, then look at back pressure?

 

[inkpot]

Hmmm? I think I may know of a local 93 parts rig......

 

[sjpitts]

It could be from excessive exhaust back pressure. But, the melted ones we have seen were from the diaphragm in the modulator failing/leaking, allowing hot exhaust into the upper chamber, melting it. In your case, try plugging off the lower, exhaust line, may solve the problem. If the plug keeps blowing off, then look at back pressure?

Do you mean plug the lower line that comes off the bottom of the EGR vacuum modulator and goes to the EGR valve? I have not yet found that hose. And do you plug at it at the valve, or at the modulator?

 

[sjpitts]

Hmmm? I think I may know of a local 93 parts rig......

Please tell me more. I have been needing to come see you guys for a while anyway

 

[cc93cruiser]

Dude, if your going to delete the egr system, do it right and throw your egr pipe that leads to the cylinder head away and be done with it, no more torchin'.

 

[sjpitts]

Dude, if your going to delete the egr system, do it right and throw your egr pipe that leads to the cylinder head away and be done with it, no more torchin'.

I would like that, but I still need to pass a visual inspection. Because mine is a 93 it won't throw a code if a "turn it off" and leave it there. But I might fail the visual inspection if I remove it altogether.

That is my guess anyway.

It would be nice if you could block it off at the exhaust and cylinder head, and just leave it there doing nothing. But I am not sure if that is really possible. Turning it off by blocking the vacuum hoses that turn it on is the next best thing.

 

[Pin_Head]

Except that won't help if your exhaust is obstructed.

 

[cc93cruiser]

Except that won't help if your exhaust is obstructed.

That's when you take a sawzall and cut those damn plugged cats and straight pipe that beeatch.........
But yeah unfortunetly you'd fail visual for sure..

 

[sjpitts]

Except that won't help if your exhaust is obstructed.

Is there a way to test for that? Would it throw a code or something?

 

[Pin_Head]

No code.
Sometimes it makes a whistling noise in the tail pipe.
The cats may rattle when you shake them.
You could separate the cats and take a look.

 

[sjpitts]

I have follow-up questions. As I noted above, this started shortly after I did the "redneck EGR bypass" technique where you loop the two vacuum hoses. The idea is that looping the two vacuum hoses turns off the EGR modulator, and thus keeps the EGR valve from opening -- and this keeps the pipe from getting so hot.

But I was looking at the FSM and saw this picture:

Looking at this picture, it seems like if you just "turned off the modulator" using the redneck method that the EGR gasses would still keep flowing --- they would just flow toward the EGR vacuum modulator.

If so, this would seem to make it so the EGR pipe still heats up, and would still be causing wiring problems-- so this method wouldn't work to solve the wiring issue as intended.

Plus, since the EGR valve never opens those gasses would always be going to the vacuum modulator--even at high engine speeds when the EGR valve would normally open-- that maybe this really did cause my exploding modulator?

What do you think of that?

If this is all true, it seems like I need to block that outlet of the EGR valve that goes to the EGR modulator. What could I block that with? It seems like a normal vacuum cap would melt?

I think I did see a thread where someone blocked the EGR pipe with a quarter. So maybe to keep the pipe from heating up you need to do that instead?

Again, what do you think?

Thanks

 

[inkpot]

The wiring issues are easily solved by tying the harness back to the bracket that was originally installed for that purpose.

 

[sjpitts]

The wiring issues are easily solved by tying the harness back to the bracket that was originally installed for that purpose.

So I take it that you are completely against this whole idea of turning off or blocking the EGR flow?

I only did it because so many threads seemed to suggest it as a way to prevent possible wiring problems. And I guess some people blame HG failures on the EGR.

Although, as I said above, I am sort of doubting that the redneck technique actually works as advertised.

Jared

PS: I don't know if my harness is properly secured as it is right now. I will take a look. I really should just come see you and Kevin for a host of reasons.

 

[madisonr34]

I looped the hose from the intake but on the modulator, I removed the hose and capped each of the vacuum ports individually instead of looping the hose. I throw the EGR code but i dont mine. 15k miles so far and no problems. Average 13 mpg.

 

[inkpot]

I figure it is easier to just put the wiring harness back to where it was originally designed to be?

 

[jatree]

It could be from excessive exhaust back pressure. But, the melted ones we have seen were from the diaphragm in the modulator failing/leaking, allowing hot exhaust into the upper chamber, melting it. In your case, try plugging off the lower, exhaust line, may solve the problem. If the plug keeps blowing off, then look at back pressure?

I have a failed modulator as well. Picking up a replacement today ($$) and going to test my EGR Valve, VSV, and the new Modulator once it is in. Is there an easy way to check for backpressure? I've read that measuring vacuum at the intake is a way to tell if there are restrictions in the exhaust system. If nothing else, I'd like to get the new Modulator in, and then drive it ~1hr to a place that can help with the exhaust/cat issues but not sure if that's a bad idea...